Thermionic relay and circuits therefor



Oct. 18, 1932. H. F. aRz-cm 1,883,520

THERMIONIC RELAY AND CIRCUITS THEREFOR Filed March 31. 1928 3 Sheets-Sheet l Oct. 18, 1932. H, F, E L 1,883,520

THERHIONIC RELAY AND CIRCUITS THEREFOR Filed March 31, 1928 3 Sheets-$heet 3 Figw. I H 11;

gwuewtoz HARRY F. B'REEKEL increasing the selectivity of the' time Patented Oct. 18, 1932 HARRY F. BERECKEL, OF CINCINNATL-OHIO THERMIONIC RELAY AND CIRCUITS THEREFOR Application fiIedMar ch 31, 1928. Serial No. 268,388.

My invention relates to a thermionic relay and circuit arrangements employed for the generation, amplification, detection and modulation of electric waves of any desired frequency, but for high frequency waves in particular.

In the use of the well known three-element thermionic relay, commonly referred to as a voltage operated relay, wherein the .con-

t-rol is by an electrostatic grid, various difficulties and inefliciencies are encountered. One of the chief obstacles to the use of such a relay as an amplifier is the tendency to oscillate due to the inherent capacity existing, between the plate and the control ele ments and the resultant voltage feed-back to the voltage operated electrode. It is an object of my invention to overcome this objectional feature by devising a current operated relay as distinguished from a .voltage operated relay, that is, a relay in which the control is accomplished principally by electromagnetic action and in which the electrostatic action plays only a minor part or may be entirely eliminated. H

In amplifier and oscillator circuits employing the electrostatic type of relay, the tuned input circuit of each relay must be formed of a relatively large inductance and a small capacity in order to secure maximum voltage variation for controlling the output energy. This necessitates the use of coils of relative- 1y large area having large distributed capacityv and, therefore, high effective resistance. With such coils it is diiiicult to avoid'magnetic coupling between coils in different circuits, and the selectivity of the tuned 01rcuits is necessarily low on account of the distributed capacity and high-effective resistance of the coils; It is another object of my invention to avoid the foregoing objections by employing tuned circuits having relatively small inductance and large capacity. In so doing, I am enabled to employ inductance coils of small dimensions, having small distributed capacity and low resistancethereby and reducing the coupling between coils in different circu ts.

I accomplish the foregoing objects byincircuits corporating the tuning inductance into the tube or relay structure in such manner that the coil functions simultaneously asa tuning inductance and as a control element of .the re:

By such an arrangement all external tun- 55 ing and coupling inductances or coils, with theaccompanying wiring, may be dispensed with, thereby resulting in a more eflicicnt and stable arrangement having high space economy. 1

Due to the small tuning inductances employed and to the elimination of external coupling devices, my system is particularly well adapted to the transmission and reception of waves of high frequency and makes possible the short wave length reception and transmission on fundamental frequencies that heretofore could not be reached except by the harmonic methods.

It is a further object of my invention to d'evise'a thermionic relay in which both the input and output control electrodes are of the inductance, form incorporated within the relay structure and functioning simultaneously as coupling and tuning devices, in addition to their functioning as'electrodes of the relay.

My invention is illustrated in the accompanying drawings in which:

Figure 1 shows the details of one formof vacuum tube'employed in my invention.

Figure 2 is a detector circuit employing the vacuum tube illustrated in Figure 1.

Figure 3 shows a second form of vacuum 3;, tube employed in my invention.

Figure 4 is a receiving and amplifying circuit utilizing the vacuum tube shown in Figure 3. I

Figure 5 illustrates a third form of vacuum tube employed in my invention.

Figure 6 is a detector circuit employing the tube illustrated in Figure 5.

Figure 7 illustrates a receiving circuit employing several stages of amplification and 5 a detector utilizing the relay shown in Figure 1.

Figure 8 shows a receiving system employing cascade amplifiers provided with common A and B batteries. 100

Figure 9 illustrates a multi-stage receiving arrangement employing vacuum tubes of the type shown in Figure 3. 7

Figures 10 and 11 are oscillator circuits employing vacuum tubes shown in Figure 1.

Figure 12 is a radio telephone transmission system employing vacuum tubes of the type shown in Figure 1.

Figure 13 is a radio telephone transmission system' employing vacuum tubes of the type shown in Figure 8.

Referring to Figure 1, I have diagrammatically illustrated the arrangement of the elements in one form of vacuum tube employed in my invention. In this figure, F indicates a filamentary cathode provided with terminal conductors F and F" adapted to connect the filament or cathode to any suitable source of heating current. 6 indicates a control element which, in the form shown, is an inductance coil of bare conductor'surrounding the filament and provided with ter- ,minal conductors C and C". Surrounding the control element is a substantially cylindrical plate element or anode P provided with a terminal conductor P.- This plate element may be formed of a continuous cylindrical surface, or it may be formed of an interrupted cylindrical surface in order to prevent losses due to eddy currents. ,The control element G is rovided with a third terminal conductor connected at the midpoint of the coil and passing through either a hole or a slot in the wall of the plate element. Instead of passing through the plate element, this connection may be brought out through the open ends of the cylindrical plate element.

Control element C is termed into a coil having considerable inductance and. relatively low resistance. The turns of the coil are spaced apart to permit the flow of electrons from the filament to the plate of the tube. The various elements of the tube may be supported in proper relation within the evacuated envelope E by structures well known to those skilled in the art relating to vacuum tubes. The principal'feature of construction of the tube of my invention is that the control element C is so constructed that when a current is passed through it, a mag- .netic field is set up at right angles to the direction of .flow of electrons from the filament F to the plate P. The envelope E is "in the art that instead of a straight filamentary cathode as shown in Figured, a looped filament of the usual construction may be employed. The control element C need not be cylindrical in shape, but may have other shapes so long as its magnetic field has the proper position and direction. Also, the

plate element need not be cylindrical in .form

but may assume other shapes.

In Figure 2, I have illustrated a detector circuit employing the vacuum tube illustrated in Fig. 1. For the sake of clearness of illustration, the elementsof the tube are shown in spaced relation, but it is understood that the elements are arranged as shown in Fig. 1. In Fig. 2, an antenna 1 is connected through a series condenser 2 to one terminal of the control element C, the other terminal of the control element being connected to ground GN. The terminal conductors of control element C are shunted externally of the tube by a variable condenser 3, which is of sufficient capacity to form with the inductance of element C a tuned circuit resonating with the wave to be received. It is understood that series condenser 2 may be dispensed with, if desired, and the entire tuning be accomplished by means of variable condenser 3 in shunt tothe control element. It is also apparent that the tuning may be accomplished solely by variable condenser 2, and condenser 3 may be omittedi The filament of the tube is heated by any suitable source of current, such as a battery 4, and the battery 5 indicates any suitable source of direct current for supplying the plate current. 6 indicates any suitable'signal responsive device, which for convenience is shown as an ordinarytelephone head set. A single pole threepositioned switch 7 is provided for the purpose ofconnecting one side of the filament circuit either to ground through a biasing battery 8 or to a midpoint tap of the control element C through the biasing battery, or switch 7 may be placed in neutral position thereby leaving the filament circuit independent of the circuits associated with the element C. As will be explained hereinafter, the biasing battery 8 may, under certain conditions, be omitted, and the filament circuit connected directly either to ground or to the midpoint of control element C by switch 7.

The operation of Fig.2 is as f0 lows With filament F energized, battery 5 will supply a normal plate current through the si a1 device 6. This normal plate current will depend upon the temperature of the filament, the voltage of battery 5, the physical arrangement and dimensions of the elements within the tube, and the voltage of biasing battery 9 in case it be used. Themost effective means of controlling the normal plate current is by adjusting the potential of one or more of the sources 4, 5 and 8. Assume that the switch 7 is thrown to the lower posi tion connecting the filament circuit to ground through biasing battery 8. This battery will maintain a definite otential between the con trol element C and lament F, and will therefore serve to determine the normal plate current flowing throu h the tube. The antenna circuit is tuned to t e desired wave length'by condenser2 or condenser 3, or by both, until" maximum current flows through controlele- P to travel in a spiral path concentric with I the filament. The amount of spiralling of the electron stream will depend upon the .strength of the magnetic field. As the field increases the spiralling increases, with the result that a certain amount of theelectrons never reach-the plate, thus -the late current is effectively decreased. The eld strengthnecessary to produce a substantial reduction in the plate current will depend upon the physical arrangementand characteristics of any particular tube. -Since the various elements are symmetrically arranged, a magnetic field set up by current flowing through the coil in either direction has the same effect upon the plate current, that is, a magnetic field in either direction will tend to cause a decrease in the normal plate current flowing through the tube. Accordingly, each oscillation of the receiving current produces a decrease in the plate current flowing-through the signal responsive device, and a series of.

wave trains will produce an effective decrease in the'averagexcurrent flowing through the signal .device and, will, therefore, produce a signal response. The magnitude of variation in the plate current or the signal response will depend upon thestrength of the signals being received, and will follow the signal strength variations.

While I believe the principal control of the electron stream is by means of the magnetic field set up by control element C, it will be signed to have a minimum amount of inductance consisting with the requirements necessary for tuning to the desired wave length,

i the potential set up by the high frequency current flowing through the control element will not be of very large magnitude. If it be desired to eliminate the electrostatic control of the element C upon the plate current flowing through the tube, the switch 7 may be transferred to the upper contact thereby connecting the filament circuit to the midpoint of the control element 0. Under this condition the-electrostatic control of the stream effected by one end of the control element is offset by the control of the opposite end, since the potential variation of the two ends of the coil are opposite with respect to the centeroperating characteristic, such currentmay be I supplied from any suitable source connected across the terminals of element C through suitable choke coils to exclude the high frequency waves. Such an arrangement is shown in connection with other figures, as will hereinafter appear. 7

In Figure 3 I have shown a second modificationof a vacuum tube employed in my invention. The construction in this case is substantially the same as the construction shown in Fig. 1, except that thecylindrical form of plate is replaced by -a plate element P in the form of an inductance coil provided with connecting terminal conductorsP' and P". It will be observed that the coil comprisingthe plateelement is in inductive relation to the coil comprising the control element, and, therefore, the magnetic field set up by current flowing through the plate coil is superimposed upon the field set up b the control element. The plate element in 1g. 3 is intended to serve notonly as an anode in the plate circuit of the tube for receiving the electron stream flowing from the filament,

but is also intended to serve as an inductive element in circuits completed between ter- Coil C may minal conductors P and P. have a mid-tap, as in Figs. 1 and 2.

In Fig. 4,1 have shown a radio receiving and amplifying circuit employing the tube illustrated in Fig. 3. In this arrangement the connection of the-antenna to the control element C is the same as in Fig. 1, except that the series condenser 52 has been omitted and an additional loading inductance 9 has been inserted in the tuned circuit comprising the control element G and variable condenser 3. The purpose of the additional inductance 9 is to increase the tuning range of the circuit beyond the maximum resonant wave length of the control element C and condenser 3" alone. A switch 10 is provided for shortcircuiting the inductance 9 in case it is not required. As explained above a battery (a) is connected across the terminals of control element C through choke coils Z) and b for the purpose of supplying a normal magnetizing current through the coil in order to secure operation upon a desired point of the characteristic curve of the tube. This additionalmagnetizing current is desirable where the characteristics of the tube make it necessar to supply an initial magnetizing field in or er to place the tube in operation upon a straight line portion of its characteristic curve for the purpose of amplification. Plate battery 5 is connected to one terminal of the plate coil P, and a variable condenser 11 is connected in shunt to the plate coil.

1 The operation of Fig. 4, is as follows:

With no signals being received there is 'a' normal plate current flowing through the tioned above. The electron stream flowing static energy picked up by the antenna into current or magnetic energy form.

In Figure 7, I have shown a receiving circuit employing several stages of amplification and a detector, utilizing the relay shown in Figure 1. The relays A A and A indicate amplifiers, and the relay D indicates a detector. The a-ntenna 1 is connected in series with the control element of amplifier A? and in series with tuning condenser 2. Energizing batteries, 4, 5 and 8 are provided for the proper energization of each relay, as explained above. The plate circuit of amplifier A is completed through the control coilmal plate current from the control element of the detector D, the plate circuit of amplifier A is completed through a choke coil .14, and the input circuit of the detector D is connected in shunt to choke coil 14 by a stopping condenser 15. The controlcoil of detector D is resonated to the received wave by variable condenser 16 connected in shunt thereto.-

Any suitablesignal responsive device'6 is connected in the output circuit of the detector relay. It will be notedthat in the case of amplifier A and A the normal plate current of. the preceding relay flows through the control coil and supplies an initial magnetizing field. .In case this field is not of sufficient strength to place the relay in proper operating condition for ainplification, a stronger magnetizing current may be supplied froni batteries 4 and 8 connected in series across the terminals of thecontrol coil by means of a choke coil 17 and a variable controlling resistance 18, Choke coil 17 prevents the short-circuiting of the received wave by the magnetizing circuit. Switches 19 are provided for the. purpose of disconnecting this auxiliary circuitin case it is not required. An initial magnetizing current, if

required, may be supplied to the control coil of amplifier A in the same way as shown.

It is obvious that any'initial magnetizing current which may be required by any of the re lays may be supplied from a separate battery as indicated in Figure 4. It is believed the operation of Figure 7 will be apparent from the description of the preceding figures- From an inspection of Figure 7 it will'be noted that thecomplete-receiving arrangement shown does not include any tuning or coupling inductances external of the tubes themselves and, therefore, the external wiringnecessary for associating the various relays is reduced to a minimum, with the consequent reduction of-the evils and 'ob ectio ns "incident to the use of such external coils and associated wiring- Due to the elimination of extraneous capacities and to the reduction of the tuning. inductances to small values, thereby eliminating the ma etic linkage between adjacent circuits, it 18 possible to employ several stages of amplification-in selectively amplifying high frequency waves without undue losses or self oscillation.

In Figure 8, there is shown a receiving system substantially like the system shown m Figure 7 except that thefilament and late currents for all the relays are supplied rom= common sources, and the relays employed are provided with cathodes of the usual looped filament construction. Also, an additional amplifier A is provided.v for the purpose of amplifying the detected low frequency current. Amplifiers A and A are supplied with initial magnetizing current by the plate current of the preceding relay. In case the characteristic of these relays is such that this magnetizing current is not required, the controlelectrodes of these two amplifiers'may be isolated from the direct current path of the plate circuit of the preceding relay in the same way that the detector D is isolated from the. plate circuit of amplifier A. It is understood, that in case it be found necessary,

additional magnetizing current may be supplied to control coils of any of. the relays by methods already discussed.

' In Figure'9, is shown a receiving circuit comprisin three stages of radio frequency amplification, a detector, and one stage of audio frequency. amplification employing relays of the type shown in Fi ure 3. The anode inductance coil of ampli er A is connected in circuit with the control coil of amplifier A'* in series with a tuning C011. denser 12. Ina like manner the anode coil 'of amplifier A is connected in circuit with the control coil of amplifier A? by a tuning condenser 13. The tuning condenser 14 associates the anode coil of amplifier A with the control coil of detector D. The three variable condensers referred to serve to tune the respective circuits to the waves being received. Stopping condensers 20, 21 and 22 are inserted in the three tuned circuits for the purpose of preventing the application of the voltage of plate battery 5 to the ,control coils of relays A A and ,D. Initial'mag-- netizing current or relays A to A is supment.

and the control coil of amplifier A is efiectively connected in shunt to the choke coil by stopping condenser 25. Since the anode coils of relays D and A serve merely as plate electrodes, the two ends of each coil have been joined together and connected in their respective plate circuits. It will be apparent that em loyed externally of the tubes themselves,

an the anode inductance of one relay and the control inductance of the succeeding relay are simultaneously tuned b a single condenser. Due to the inductlve relation between the control coil and the anode coil of each relay, there will be a direct transfer of ener from the input to the output circuit by direct induction, and b properly adjustin the repeating action 0 the relay to coinci e in base relation with the energy transferred 'rectly, the two energies may be made to assist and augment each other.

In Figures 10 and 11, I have illustrated oscillator circuits employing the vacuum tube shown in Figure 1. In these arrangements, the filament is heated by a battery 4, and one side of the filament circuit is connected to the midpoint tap C of the control coil O. This connection is made directlywithin the tube in the arrangement shown in Figure 10, but it is made externally of the tube in Figure 11, and may include a biasing battery 8. The plate battery 5 shunted by a. by-pass condenser is connected to one terminal of the control coil O and to the plate element P. With this arrangement the path of the plate current extends from one side of the filament through one-half of the control coil O,

through the plate battery 5 to plate P, and

through the space discharge path to the fila- The frequency determining circuit of the oscillator includes in each case the control coil C, a variable condenser 2, and the antenna 1. The condenser indicated in dotv ted lines at 1 indicates the effective capacity of the antenna 1. In both these arrangements, it will be seen that the frequency determining circuit comprises the input circuit of the oscillator, and the output circuit is coupled 1 to the input circuit by having the plate cir cuit completed through a portion of the con trol coil C. Due to the common coupling between the output and input circuits, any oscillations established in the frequency determining circuit will be maintained by energy supplied from the output circuit which, in turn, is under the control of the frequency determinin circuit.

It is obvious that the coupling between the output circuit and the fre uency determining circuit of the oscillators s 1own in Figures 10 and 11 may be extended to include the entire control coil O, instead of only half of the coil as shown. The inductance control elements shown in these arrangements serve three functions simultaneously, that is, (1) .as resonating inductances in the frequency determining circuit, (2) as control elements of the thermionic relay, and (3) as coupling inductances-linking the output circuit with the input circuit.

The arrangements shown in. Figures 10 and 11 may be employed for heterodyne reception of continuous waves by providing a signal responsive device in the plate circuit, or they may be used as transmitting oscillators b providing suitable modulating or keying evices well known to thoseskilled in the art.

In Figure 12, I have shown a radio telephone transmission system comprising an oscillator O and a modulator MT. The frequenc determining circuit of oscillator O inclu es in series the antenna 1, the capacity of which is indicated by the dotted condenser 1', variable condenser 2, control element O, and a variable external inductance The ocillating circuit may be tuned to the desired wave length by either condenser 2 or the variable inductance L. One terminal of the filament F is connected to the oscillating circuit at a point between the control element O and inductance L through a biasing battery 8. It is understood that the biasing battery 8 ma be omitted when the characteristic of the tu e does not require the same. The plate circuit for the oscillator extends from one terminal of the filament through biasing battery 8, variable inductance L, plate battery 5, audio frequency choke coil AC, radio frequency choke coil RC, to the plate P. The two chokev coils and plate battery 5 I are shunted by a b ass condenser K. The plate circuit of mod iil dtor MT is completed from one side of the filament through plate battery 5, choke coil AC to plate P of the modulator tube. The control coil O of the modulator tube is connected in circuit with a microphone M and an energizing battery Ba.

Operation of Figure 12 is as follows; Oscillations established in the frequency determining circuit control the plate current of the oscillator in accordance with the oscillating vcurrent flowing through the control coil, and since the plate current is completed through inductance L, which is also included in the oscillating circuit, the plate circuit feeds back suflicient energy to the oscillating circuit to sustain the oscillations continuous- 1y. Operation of the'microphone M causes the plate current of modulator MT to vary in accordance with the signal operating the microphone, and the varying platecurrent establishes corresponding potential variaand variable condenser 11 will, therefore, re-

1,sss,52o

tions across the choke coil AC. Since the choke coil AC is connected in the late circuit of the oscillator O, the potentia variations across this coil will produce corresponding variations in the plate current of the oscillator, with the result that the generated oscil-- lations are varied in amplitude in accordance wlth the slgnal operating the microphone.

' It is apparent that the modulating arrangement shown in Fig. 12, maybe applied tothe oscillators shown in'Figs. and 11.-

In Figure 13, I have shown a second radio tele hone transmission circuit in which' the osci lator employs a vacuum tube of the type shown in Figure 3. Y In this arrangement antenna 1 is connected 111 a tuned circuit 111- cludlng variable condenser 2 and control (2011 C of oscillator O, the 'equi'valentcapacity of the antenna belng represented by dotted condenser 1'. The plate circuit of the oscillator is completed from one side' ofthe filament throughbiasing battery 8, plate battery 5, choke coil AC, choke coil BC to one side of plateor anode coil P. A variable condenser 11 is connected in shunt to the anode coil P. A by-pass condenser K is connected around plate battery 5 and choke coils RC and AC. The connection of the modulator NT is same as-shown in Figure 12. I The operation of Figure 13 isas follows:

The antennacircuit is tuned to the desired wave length by adjustable condenser '2. As

explained hereinbefore, coils C and P are in inductive relation with each other within the oscillatortube, and oscillating current set up in the tuned circuit comprising the coil P act upon the tuned antenna circuit through coil C. By'proper adjustment of condenser 11 this reaction may be made to have proper phase relation for sustaining the oscillations establishedin the-anten'na'circuit. As ex.

plained in connection with Figure 12, operatgon of microphone M causes potential variations across the audio frequency choke coil AG in. accordance with the signal characteristics beingtransmiti'ed, and these variations T produce corresponding variations in the plate current of oscillator 0, thereby resulting'in a' modulation of the waves radiated from antenna 1. It will be apparent that the vacuum tube shown in Figure 5, may be employed in the oscillator circuit in Figure '13.

. In the systems shown in Figures 12 and 13, ,modulation is accomplished electromagneti- -cally by the direct application of the microphone current to the control coil of the modulator tube, and without the use of external transformers inserted between the microphonecircuit and the modulator.

From the foregoing description of in vention, it will be seen that by employingtuned circuits having a relatively high ratio of capacity to'inductance for anygiven frequency, I obtain an effective reduction of g l the un- I desirable distributive capacity and effective.

resistance in the circuits, thus making possible greater selectivityin tuning. the. circuits ,to any given frequency to the exclusion-of others not wanted. Z

?By my invention, I have further effected a reduction of internal and external electromagnetic and electrostatic coupling effects through the combination of the resonating inductance and control element in one nnit,,.

thus reducing the tendency for inherent or self-oscillation of the relaycircuit.

It is apparent to one skilled in the art that many-changes in the details of the specific arrangement shown and described, may be made without departing from the scope of my invention. Havlng thus descr ibed my invention and illustrated its use, what I claim as new and "desire to secure by Letters Patent, is:

1. In a short wave signallingsyst em, a

thre electrode vacuum tube comprising a cathode, an anode, and a. control element comprising an inductance coil interposed in the discharge path between the anode and cathode and arranged to magnetically control the electron emission from said cathode, an input circuit includin saidcoil connected directly amplifier, a three eleloo therewith, means for tuning the input circuit to produce maximum current in said control element, and a signal responsive device,in the anode circuit of said tube,

3. In a short wave signalling system,.'a three-element vacuum tube comprising a cathode, an anode, and acurrent operated control element com' rising an inductance coil interposed in the ischarge path between the anode and cathode, an'inputcircuit including said coil connected directly in series therew1th and a space current circuit for said tube lncluding at least a portion of said controlcoil. 4. An electric relay comprising an evacuated envelophaving a cathoplle and an anode mounted therein in spaced re ation, a current operated control element interposed between the anode and cathode comprising an inductance coil arranged to magnetically control the electron emission from said cathode, an

input circuit including said coil, and means for tuning said inputcircuitto establish current resonance within said control coil.

5. An electric relay comprising an evacuated envelope having a cathode and an anode mounted therein in spaced relation, a current operated control element interposed between the anode and cathode and arranged to magnetically control the electron emlssion from said cathode, an input circuit including said .control element, and means for tuning the input circuit to establish current resonance within said control element.

6. An electric relay comprising an input circuit including an inductance coil mounted within an evacuated envelop, an electron emitting cathode and an anode mounted in spaced relation within the evacuated envelop to establish an electron stream at right angles to the magnetic circuit of said coil whereby said coil magnetically controls the electron emission of said cathode, an output circuit includ- 0 ing the cathode, the anode and a source ofcurrent, and means for tuning the input circuit to establish current resonance within the inductance coil- 7. An electric relay comprising an evacuated envelop, two inductance coils mounted in inductive relation to each other within the envelop, an electron emitting cathode mounted in spaced relation to said coils, an input circuit including one of said coils arranged to magnetically control the electron emisslon .from said cathode, and an output circuit including the cathode, the other of said coils as an anode, and means -for establishing a space current between the anode and cathode.

8. 'An electric relay comprising an evacuated envelop, two inductance coils mounted in inductive relation to each other within the envelop, an electron emitting cathode mounted in spaced relation to said coils, an input 40 circuit connected acrossxone of said coils, a space current circuit extending from one terminal of the second coil to one terminal of said cathode and including a source of current, and an output circuit connected in shunt to said second coil.

,9. An electric relay comprising an evacuated envelop, two inductance coils mounted in inductive relation to each other within the envelop, an electron emitting cathode mounted in spaced relation to-said coils, an input circuit connected across one of said coils, a

. spaced current circuit extending from one terminal of the second'coil to one terminal of said cathode and including a source of ourrent, an output circuit connected in shunt to said second coil, andim'eans for tuning said output circuit.

4 10; An electric relay. comprising an evacuated envelop, two inductance coils mounted I in'inductive relation to each other within the circuit, a space current path extending from the second coil as an anode to the cathode and including a source of current, an output circuit connected in shunt to the second c011, and means for tuning said output circmt.

. 11. An electric relay comprising an evacuated envelop having a cathode and an anode mounted therein in spaced relation, a current operated control element interposed between the anode and cathode, an input circuit connected across said control element, means to establish space current between said anode and cathode, and means to maintain said control element at a definite potential with respect to said cathode.

12. An electric relay comprising an evacuated envelop having a cathode and an anode mounted therein in spaced relation, a current operated control element interposed between the anode and cathode comprising an inductance coil, an input circuit including said coil, means to establish space current between the anode and cathode, and a conductive path connected between the cathode and the midpoint of-the control coil.

13. Anelectric relay comprising an evacuated envelop having a cathode and an anode mounted therein in spaced relation, a current' operated control element interposed betweenthe anode and cathode comprising an inductance coil, an input circuit including said coil, means to establish space current between the anode and cathode, a conductive path conmeeting the cathode to the mid-point of the control coil, and a source of otential in sald path for maintaining a definite potential if- :t'erence. between the cathode and control e ement.

14. In an amplifying system, a plurality of thermionic relays each comprising a cathode, an anode and a current operated control element interposed in the space discharge path between the cathode and anode, a circuit directly coupling said relaysin cascade including the space current path of one tube and the control element of another, and a signal device associated with the output circuit of the output relay.

15; In an amplifying system, a plurality of thermionic relays in cascade, each comprising a cathode, an anode and a current operted control element interposed in the space discharge path between the cathode and anode, a tuned circuit connected in the .output circuit of each relay and including the control element of'the succeeding relay in series circuit relation therewith.

16. In an amplifying system, a plurality of thermionic relays in cascade, each comprising a cathode, an anode, and a control electrode interposed between the anode and cathode, at least one of said electrodes comprising an inductance coil, a tuned circuit connecting the output circuit of each relay to the input of the succeedin relay, thesa-id inductance coil electrodes 0 the relays constitutin the sole inductive elements in said tuned circuits.

17. In ,an amplifier, a series of thermionic relays in cascade each comprising an electron emitting cathode, an anode comprising an inductance coil in spaced relation thereto,

a current operated control element compris-' ing an inductance coil inter osed between the cathode and anode, close for coupling together successive re ays each comprising the anode of one relay and the control element of a succeeding relay connected in series in said loop circuit.

18. In an amplifier system, a plurality of thermionic relays in cascade relation, each of said relays comprising a heated cathode,

an inductance coil serving as an anode, and a second inductance coil interposed in the space discharge path between the cathode and anode serving as an element to magnetically control the electron emission from said cathode, an foutput circuit for each relay includin anode coil 0 one relay and the control coil of the succeeding relay, and a condenser in each output circuit for tuning the circuit to the received wave.

19. In an amplifier system, thermionic vacuum rela s each comprisin an electron emitting cat ode, an anode ormed of an inductance coil in spaced relation to said cathode, a control element formed of an inductance 'coil interposed between said cathode and anode, series circuits each comprising the anode coil of a relay a variable capacity, and the control coil 0% a second relay constituting a tuned circuit serving to couple adjacent relays in cascade relation.

20. in an amphfier, a -plurality of thermionic relays in cascade relation, each relay comprising an evacuated envelo ,two inductance coils mounted in inductive relation to each other within the envelope, an electron emittin cathode mounted in spaced relation to said coils, and con ling circuits interposed between adjacent cuit includin in series circuit relation an inductance coll oi one relay and a coil of the succeeding relay. a.

In testimony whereof I have hereunto signed my name. HARRYF. BRECKEL.

circuits 1 in serles circuit relation the ays, each cir- 

